1. Field of the Invention
This invention relates to control devices for use with high-pressure steam cleaning or water cleaning systems. In particular, it relates to an electrical control mechanism for controlling the pumps and mixing valves required in such systems.
2. The Prior Art
It has been common in the prior art in high-pressure pumping systems which develop pressures of 1,000 to 2,000 lbs. per square inch under normal operation with the control valves open, to use trigger valves of the type represented by a German manufactured device known as a Spritzpistole ST 700, a commercially available trigger shut off gun manufactured by Suttner Technik and marketed under the name Suttner pistol in the United States by an importer known as Kurt Wilms. The configurations of the systems which use the Spritzpistole ST 700 basically involve a high-pressure pump associated with a tank containing steam or hot water or some appropriate solvent with or without some sort of mixing apparatus which includes some sort of a soap or other cleaning agent. The liquid, detergent mixture is pumped out of the tank by the high-pressure pumps through flexible hoses and into the base of the Spritzpistole ST 700. Valving is accomplished by a needle valve conventionally manipulated on and off using a trigger having a lock mechanism with a spring-loaded adjustment. When the valve in the Spritzpistole ST 700 is closed, a pressure surge is immediately experienced by the flexible hosing connecting the pistol to the high-pressure pumping mechanism. This impulse surge can far exceed the normal 1,000 to 2,000 lbs. per square inch pressure exerted by the pumps and is a continual source of wear and tear on the hoses and plumbing. In the prior art, this problem was attempted to be alleviated by using what is known as a by-pass unloader valve in the pumping system. This unloader valve detects the impulse which is present in the flexible hose and which has traveled back to the pump from the Spritzpistole ST 700. Upon detection of this high-pressure impulse, the by-pass unloader valve trips and permits a flow of fluid around the pump thereby substantially minimizing or eliminating this high-pressure impulse. That prior art solution to the high-pressure impulse problem suffers from two chronic and recognized defects. One chronic defect is the fact that a momentary high-pressure impulse is still applied to the structure of the Spritzpistole ST 700 as well as to the flexible hoses connecting the pistol to the pumping apparatus. The duration of this impulse corresponds to the time involved until the by-pass unloader valve kicks in. A second problem has been due to the structure and nature of the by-pass unloader valves themselves. These valves are always a continual source of maintenance and reliability problems and require additional expense in terms of extra plumbing and the price of the valve itself. If should be noted also that even with the by-pass unloader valve solution to the problem, there is always a pressure applied to the flexible hosing even if the Spritzpistole ST 700 is turned off. This, in itself, represents to a certain extent a reliability problem in case one of the hoses should suddenly rupture, even if the by-pass unloader valve has functioned properly, there will still be a stream of fluid emanating from the rupture in the hose.